1. Field of the Invention
The present invention relates to a stator coil constructed by joined conductor segments for rotary electric machines and a method for manufacturing the same.
2. Description of the Related Art
There have been disclosed joined conductor segment stator coils, wherein a plurality of conductor segments inserted into slots of a stator core are sequentially connected one by one. For example, a method for manufacturing the joined conductor coil (joined conductor segment stator coil) by utilizing nearly U-shaped conductor segment in JP No. 3118837.
In JP No. 3118837, legs of a pair of the nearly U-shaped conductor segments are inserted into an entrance of, and are projected from the opposite exits of, a pair of slots distant from each other by a magnet pole pitch of a rotor. Then, the projected legs are bent toward the circumferential direction of the rotor and are sequentially joined together.
Therefore, the conductor segment comprises: a nearly U-shaped (nearly V-shaped seen along the circumferential direction after bending process as explained below) head portion; a pair of slot conductor portions which are inserted into a pair of slots, and are staying in the pair of slots; and a pair of projected end portions projected from the other end of the pair of slots. Further, the tips of the projected end portions in the pair are joined with each other. Here, in the present specification, the projected end portion together with the slot conductor portion is sometimes denoted as a leg of segment. The head portion of segment is a head side coil end of the stator coil, while the projected end portion is an end side coil end.
Further, there are disclosed also in JP No. 3118837 co-axially disposed two rings for holding four legs of a pair of the small and large segments. Here, the large segment surrounds the small segment. The rings are relatively rotated in order to form a oblique end portion (a pair of legs oblique toward the circumferential direction of the rotor).
Further, it is disclosed in JP No. 310470 that a projected end portion is welded with another project end portion adjacent along the radial direction and further a binding member is held between the two projected end portions adjacent with each other in the circumferential direction in order to stabilize their positions.
Next, an exemplary method for manufacturing the joined conductor coil as disclosed in the above-mentioned prior art documents is explained.
First, a required number of pine needle segments are prepared and are bent to have the U-shaped heads. Then, the segment legs are bent along the circumferential direction by a magneto pole pitch. The segment sets are arranged along the circumreferential direction in order to simultaneously insert them into all the slots of the core. The two rings (co-axially disposed) with a plurality of holes as shown in FIG. 3 in JP No. 3118837 may be employed. Concretely, segment legs are inserted into the outer and inner rings at the same circumferential direction and then the inner and outer rings are relatively rotated in order to deform the head portion in such a manner that the head portion is made open like a V-shape.
Further, a process step follows for inserting the V-shaped deformed segments which are arranged along the circumferential direction into slots of the stator core. Concretely, holding the head portions, the segment sets are pulled out from the rings and are inserted into the slots.
Further, a process step follows for bending, preferably by a half pitch of the magneto pole, the projected end portion along the circumferential direction. The two rings (co-axially disposed) with a plurality of holes as shown in FIGS. 4 and 5 in JP No. 3196738 may be employed for the above-mentioned bending step. The projected end portion is inserted into the holes, then the inner and outer rings are relatively rotated by a half pitch of the magnet pole and then the projected end portion is bent by the half pitch along the circumferential direction. The radius of curature at the bending point can preferably be made larger, if the rings are pressed along the axial direction toward the projected end portion. Further, a process step follows for welding the projected end portions each other in a prescribed order.
Thus, phase coils, e.g., three phase armature coils are endlessly formed. Terminals for each phase are formed by cutting the head portion of the segment. If the terminal is made long beforehand, the long terminal can be utilized for a crossover for a neutral point. It is noticed that the terminal is provided at the head portion side, because the long terminal wire is obstructive against the welding of the projected end portions.
The joined segment stator coil as manufactured by the above-explained processes has been employed for a stator coil of alternating current dynamo for automotive vehicles.
However, the conventional joined segment stator coil has disadvantages as stated below.
A pair of the projected end portions projected from the stator core are positioned at the same circumferential position and at different radial positions. Then, by the relative rotation of the rings, the projected end portions are relatively rotated in a reverse direction with each other and are bent along the circumferential direction.
The end portion is bent down linearly and obliquely (both along the circumferential and radial directions) in such a manner that the tip of end portion after bending be connected by the shortest distance with a part of a slot conductor portion which is not bent.
This is similar, when the head portion is bent down.
Therefore, the conventional manufacturing process has a disadvantage that the oblique head portions and oblique end portions, particularly those at innermost radial side go beyond the inner circumferential surface of the stator core, thereby making it difficult to insert the rotor into the inside of the stator core and causing an interference of oblique head and end portions with a cooling fan provided on an end surface of the rotor.
As already mentioned, the oblique head and end portions extend not over the circumferential surface, but over a plane. This means that the square shaped conductor segment is bent toward the square cross section at a border portion of the oblique head portion and a tip of head portion, at a border of the oblique end portion and a tip of end portion, at a border of the oblique head portion and slot conductor portion and at a border of the oblique end portion and slot conductor portion. Accordingly, the conventional manufacturing process has another disadvantage that a great stress is generated in the insulating coating at the border portion, thereby degrading an insulation of the segment. This may be a possible disadvantage, when the conventional joined segment stator coil is to be applied for a high voltage rotary machinery such as a vehicle motor.